Hydrofoil steering, adjusting and retracting mechanism



J. BADER May 19, 1959 HYDROFOIL STEERING, ADJUSTING AND RETRACTING MECHANISM Filed Aug. 3l, 1956 4 Sheets-Sheet 1 J. BADER Maxv 19, 1959 HYDROFOIL STEERING, ADJUSTING AND RETRACTING MECHANISM Fiied Aug. s1. 195s 4 Sheets-Sheet 2 INVENTOR JOHN BADER ATTORNEYS J. BADER HynRoFoIL STEERING, ADJUsTING AND RETRACTING MEcHANIsM Filed Aug. s1, 195s 4 Sheets-Sheet 3 INVENTOR JOHN BADER 2 /8- ATTORNEYS 2,887,081 HYDROFOIL STEERING, ADJUSTING AND RETRACTING MECHANISM Filed Aug. 51, 1956 J. BADER May 19, 1959 4 Sheets-Sheet 4 l INVENT OR JOHN BADER BY i /fm/ United States Patent O HYDROFOIL STEERING, ADJUSTING AND RETRACTING MECHANISM John Bader, Washington, D.C. Application August 31, 1956, Serial No. 607,528 7 claims. (ci. 114-665) j (Granted under Title 35, U.S. Code (1952), sec. 266) #The invention described herein may be manufactured and used .by or'for the Government of the United States of America for governmental .purposes without the paym'ent of. any royalties thereon'or therefor.

This invention relates to improvements in hydrofoil craft and in particular it'relates to steering, angle of attack control and indication, and to retraction of hydrofoils.l I

Existing mechanisms for supporting forward foils on a hydrofoil craft are mounted on the ends of fixed arms eX- tendi'ng from the sides of the craft. Such mechanisms make no provision for steering by the forward foils. With such mechanisms, any adjustment to the angle of attack of the foils is awkward and cumbersome. Such mechanisms are relatively inaccessible and the lxed arms are a constant source of annoyance and damage while the craft is lying alongside a dock or the like. The structures used heretofore allow the foils to be jarred out of adjustment, and no simple check is possible for realignment while waterborne. Realignment is a tedious process which, with existing mechanisms, can be done only after the craft has been hauled from the water.

In a companion patent application of Harold Boericke, lr. and John Bader, Serial No. 607,529, tiled concurrently herewith, in which applicant is a joint inventor, there is disclosed a novel hydrofoil craft wherein hydrofoils not only support the craft in motion but are used also as rudders for steering. In accordance with .the above joint invention, movement of the steering wheel within a steering range causes a pair of hydrofoils to move in opposite directions fore and aft of athwartship. The angle of attack of the foils and therefore the amount of` lift produced by the foil is automatically adjusted during the steering and responsive thereto. The angle-of attack of `the foils may be manually adjusted atany time.

Movement of the steering wheel beyond the steering range causes .the hydrofoils to be retracted clear of the water for hull-borne operation and docking.

j, 4. ln'accordance with the instant invention, which may be considered another embodiment or modication of the above joint invention, there is provided a mechanism for supporting and steering a craft by hydrofoils; for manually` and automaticallyadjusting the angle of attack of the foils; and for retract-ing the hydrofoils for hull-borne operation and docking,` The specific. mechanism disclosed includes a rst hydraulic system energized by movement of the steering wheel for operating a mechanism which moves a pairof hydrofoils in opposite directions fore and aft of athwartShilJwithin a steering range for steering the craft. A second hydraulic system retracts the hydrofoils for hull-borne operation and docking.

The instant invention `includes a number of `common features and a number ofcontrasting features with the above joint. invention, as pointed out in detail hereinafterlsz 1v ,zA-.general objcctof the instant 4invention is theproice vision of mechanism for steering by means of hydrofoils', for controlling and indicating angle of attack of the hydrofoils, and for retracting the hydrofoils clear of the water.

Another object of the invention is the provision of interconnected mechanisms for hydrofoil steering and retracting.

Another object of this invention is the provision of simplied mechanisms for hydrofoil steering and retracting.

The invention, together with the above and other objects and advantages thereof, is set forth in more technical detail in the following description and accompanying drawings, wherein:

Fig. l is a schematic `top plan view, partly insection, of a water craft showing a pair of hydrofoils attached to opposite sides of the hull and operating mechanisms for manipulating the foils in accordancel with this invention;

Fig. 2 is a transverse vertical section through one side of the hull and showing, in front elevation, one hydrofoil and its support and operating mechanism;

Fig. 3 is an enlarged side elevation of a part of the operating mechanism shown in Fig. 2;

Fig. 4 is a transverse vertical section taken on line 4--4 of Fig. 9;

Fig. 5 is an elevation similar to Fig. 3, with certain parts in different relative positions;

F Fig. 6 is a transverse section taken on line 6 6 `of F Fig. 7 is a transverse section taken on line 7--7 of Fig. 8 is a transverse section taken on line 8-8 of Fig. 4; and

Fig. 9 is a side elevational view of the structure shown in Fig. 2, and showing in broken lines the relative retracted position of a hydrofoil.

In Fig. l of the drawings, for purposes of illustration, there is shown a water craft 10 having a pair of hydrofoil mechanisms 12 and 12 mounted on opposite sides of the hull near the bow thereof. Suitable aft hydrofoil mechanisms, not shown, may be mounted near the stern of the craft. For steering the craft, hydrofoil mechanisms 12 and 12 are operated by a pair of hydraulic rams 14 and 14', respectively. A hydraulic system including a pair of conduits 16 and 18 having branches 16a and 16b, and 18a and 18b, respectively, connect opposite ends of the rams 14 and 14' to opposite ends of a steering cylinder 20. The steering cylinder is mounted on a control box 22 and is provided with a piston 24 and a piston rod 26, which piston rod is connected to a gear rack 28 for reciprocation thereby and therewith. A pinion gear 30, mounted on the forward end of a steering shaft 32, meshes with rack 28. The steering shaft is journaled on the control box and has a steering wheel 34 mounted on the` aft end thereof. Thus, as pointed out in detail hereinafter, clockwise rotation of the steering wheel causes piston 24 to move inward of cylinder 20 and thereby force hydraulic uid through conduit 18 and branches 18a and 18b into the aft end of ram 14 and into the forward end of ram 14'; with the result that the hydrofoil mechanism 12 is rotated aft of the athwartship position and hydrofoil mechanism 12 is rotated forward, whereupon the craft maneuvers a right or starboard turn. Counterclockwise rotation of the steering wheel causes opposite ow of duid through the hydraulic system and opposite rotation of the hydrofoil mechanisms, resulting in a left or port turn `of the craft.

Referring still to Fig. l, for retracting the hydrofoil mechanisms 12 and 12, a solenoid-operated plunger 36 is mounted on the control box and includes a piston 31 t mounted within a cylinder 38, which cylinder has a pair asegurar of conduits and 41 connected to opposite ends thereof. Conduit 40 is provided with a pair of branches 40a and dill; connected, respectively, rto the aft ends of a pair of retracting rams 42 and 4 2. Conduit 41 is provided with a Pair Of branchesltzA 41h connected, respectively, to the forward ends of retracting rams 42 and 42.

The solenoid-operated plunger, when deenergized, is spring-biased to its inner position, as shown in Fig. 1, and when energized, piston 37 is forced outwardly of cylinder v38 and hydraulic fluid is forced through conduit 40 and branches 40a and 40b into the aft ends of retracting rams 42 and'42 behind the pistons therein, with the result that the pistons are forced inward of the cylinders and through connecting arms and gears, as described in detail hereinafter, the hydrofoil mechanisms 12 and 12 are each rotated forward of the craft and kinto an upsidedown position against the sides of the hull thereof, as shown in broken lines in Fig. `9. The solenoid-operated plunger is connected in a suitable electric circuit, and any suitable means, such'as a conveniently located switch, not shown, may be used for energizing the solenoid.

Thus, the hydrofoil mechanisms 12and 12 are rotated in opposite directions fore and aft of athwartship by one hydraulic system for steering the craft, and are'rotated forwardly of the craft by a second hydraulic system for retracting the hydrofoils. The hydrofoil mechanisms are identical, except that they are of opposite hand. Therefore, only one such mechanism, 12, will be described in detail.

Referring now to Figs. 2 and 4,.hydrofoil mechanism 12 includes a substantially triangular-shaped frame 50 mounted on the hull of the craft by a pair of gud-geons 51 and 52. Frame includes a near-vertical tubular member 53, a horizontal tubular member 54 and connecting struts 55 and 56. A near-vertical shaft 58, that passes through tubular member 53, mounts the frame on the gudgeons for rotation about a near-vertical axis. A horizontal shaft 59 passes through tubular member 54 of the frame and has a hydrofoil 60 rigidly attached thereto for rotation therewith. A bevel gear 62 attached to the inboard end of horizontal shaft 59 meshes with a companion bevel lgear 63 formed on the lower end of nearvertical shaft 58.

The hydrofoil may be of any desired form, however, for purposes of illustration, it is shown here as a diamond-shaped foil in accordance with the invention of Harold Boericke, lr., and described in his application, Serial No. 555,212, filed December 23, 1955.

As shown in Fig. 2, the hydrofoil comprises a unitary structure includingv an upper .or inverted V-shaped foil 64, a lower V-shaped foil 65 and a horizontal foil and brace 66. Therhydrofoil is attached to the outboard end of shaft 59 by a strut 67, which, as shown in Figs. 2 and 9, extends upward and aft from the top V and terminates in a collar 68 rigidly secured to shaft S9, and at the inboard corner, the hydrofoil is supported by a strut 69 also rigidly secured to shaft 59. Thus, as shown in Figs. 2 and 9, the hydrofoil is supported on a horizontal axis on a line to the rear of the plane of the foils so that lift forces of the foils tend to rotate the bottom of the hydrofoil forward. This tends to counter-balance the effects of drag forces tending to rotate the bottom of the hydrofoil aft. In this manner, hydrodynamic balance is obtained. For a more detailed description of the diamond-shaped hydrofoil and modifications thereof, reference maybe had to the above patent application of Harold Boericke, lr., Serial No. 555,212.

Returning to Figs. 2 and 4, the frame 50, and hydrofoil 60 attached thereto, is made to rotate ywith and about the near-vertical shaft 5S by a steering arm 70, as described hereinafter. Arm 70 has a cylindrical outboard portion 70e that surrounds the upper end of frame member`53 etltlis slidably. keyed thereto `by mating keyways and` projetions' formed inadjacent surfaces thereof and indicated generally at 71 in Fig, 8. The inboard end of arm 70 craft.

is pivoted, as by a pivot pin 72 (Fig. 7), to a bifurcated end 73 of a piston rod 74, which piston rod is attached to a piston 75 (Figs. l and 9) within a cylinder 76 of hydraulic ram 14. So that the cylinder of the hydraulic ram may be free to move with movement of the piston and piston rod, the cylinder is pivoted to the deck of the craft by a pivot connection 78.

An arm 80, for manually adjusting the angle of attack 0f the hydrofoil, is mounted on top of steering arm 70 and has an outboard end A thereto that surrounds shaft 50 and is releasably attached thereto by `a splined sleeve (Fig. 7). The inboard end of arm 80 is formed as a segment of a gear 82 that meshes with a worm gear 84. Gear 84 is provided with an integral shaft `35 journaled in a pair of supports S6 formed on steering arm 7 0. A crank 07, for manually rotating the worm gear and through it the adjusting arm 80, is mounted on one end of shaft 85.

The upper portion of near-vertical y'shaft 58 is formed with a portion 58a (Figs. 4-'and 7) yof reduced diameter upon which is mounted thesplined `sleeve 90. A safety or shear pin 91 attaches the splined vsleeve to the shaft for rotation therewith. As v shown in Fig. 7, theouter surface of the splined sleeve 4and the inner surface ofarm 80 are formed with mating projections and depressions, indicated generally at 92, whereby the arm may slide vertically relative to the reducedportion 58a of the nearvertical shaft and it is keyed to the shaft for rotation therewith. Thus, adjusting arm 80 is arranged to ,move with and relative to steering arm 70.

As shown in Figs. 4 and 6, a retracting arm 100 is pivotally mounted on a post 101 that is secured to the upper gudgeon 51. Arm has an inboard end pivotally con.- nected, as by a pivot pin 102, to a bifurcated end 103 of a piston rod 104, which piston rod is attached to a piston 10S (Figs. 1 and 9) within cylinder 106 of retracting ram 42. So that cylinder 106 may be free to move with movement of the piston and piston rod, the cylinder is pivoted to the deck of the craft by a pivot connector 107. The outboard end of retracting arm 100 is formed as a gear segment 110 (Fig. 6) which meshes with a ring gear 111 mounted for rotation on the upper portion of frame member 53 (Fig. 4). The ring gear is formed with diametrically opposite cam surfaces 112 on the lower `surface thereof, only one of which is shown in Figs. 3 and 5 which contact and ride upon similar cam surfaces 113 formed on an upper cylindrical surface of gudgeon 51 (Figs. 3 and 6). A second pair of cam surfaces 114 are formed on the upper surface of `the ring Agear andare adapted to contact a pair of keys A115 secured by pins 116 to the top surface of frame member 53 (Figs. 4 and A6).

The cylindrical portion or outboard end of steering arm 70 is provided with a pair of keyways 70e (Fig. 3') in the lower surface thereof to receive the keys 115.l As shown in Fig. 4, the ring gear 111, steering arm 70 and angle of attack adjusting arm 80 are releasably and slidably held in contact with each other on the upper portion of gudgeon 51, frame member53 and shaft 58v by a compression spring 116 held in place 'by a Washer 117 and nut 118. As pointed out hereinafter, the ringl gear with the cam surfaces on upper and lower surfaces thereof and the cam `surfaces on the upper portion ofthe gudgeon function as a clutch for locking the frame member 53 to the near-vertical shaft 58 for rotation therewithand for releasing the frame member for rotation relative to the shaft.

In operation, with the hydrofoils athwartship, as shown in Fig. 1, clockwise rotation of the steering wheel, through the rack and pinion,causes piston 24 to be moved inwardly of cylinder 20 andhydraulic uid to be forced from the cylinder through conduitf18 and branch 18a into hydraulic ram 14 in front of piston 75 therein,'with the result that the piston is forced outwardly of the cylinder and hydrofoil mechanism 12 is rotated aft ofrthe Simultaneously with the l forcing o'f uid :through ass'aosfi branch, 18a, fluid is forced through branch 18b into hydraulic ram 14 behind piston 75 therein, with the result that this piston is forced inwardly of the cylinder and hydrofoil mechanism 12 is rotated forwardly to the craft; thus, the craft makes atstarboard turn. Counterclockwise rotation of the steering wheel causes fluid to be forced through conduit 16 and branches 16a and 1611 into rams 14 and 14 resulting in forward rotation of hydrofoil mechanism 12 and after rotation of hydrofoil mechanism 12'; whereupon, a port turn is maneuvered. The steering range of the hydrofoil mechanisms is approximately eight degrees fore and aft of athwartship. It will be noted that the hydraulic system thus far described constitutes a closed circuit so that the forcing of fluid from one end of a cylinder causes lluid to llow into the opposite end thereof, and vice versa.

With the clutch engaged, as shown in Figs. 4 and 5, frame 50, near-vertical shaft 58, horizontal shaft 59, bevel gears 62 and 63, and hydrofoil 60 are held xed relative to each other, so that through the steering range of approximately eight degrees fore and aft of athwartship these components rotate about the near-vertical axis as a unit. The steering range of movement of the piston 75 fore and aft the cylinder 76 of hydraulic ram 14 is approximately that shown in Figs. l and 9. That is, the capacity of hydraulic cylinder 20 (Fig. l1) is such that, with maximum clockwise movement of the steering wheel in the steering range, suicient uid is forced from cylinder,20 through conduit 18 and branch 18a into cylinder 76 to force piston 75 from the mid-position shown in Figs. l and 9 to the inner end of the cylinder. Conversely, with maximum counterclockwise rotation of the steering wheel in the steering range, suicient fluid is forced from cylinder 20 through conduit 16 and branch 16a into cylinder 76 to force piston 75 from the position shown in Fig. 9 a like distance outwardly of the cylinder.

In retracting the hydrofoils it is preferred that the hydrofoil mechanisms be in the athwartship positions shown in Fig. 1. With the mechanisms so positioned, solenoid plunger 36 is energized, whereupon piston 37 is forced outwardly of cylinder 38 (Fig. l) with the result that hydraulic fluid is forced through conduit 40 and branches 40a and 40b into the aft ends of cylinders 106 and 106,`respectively, behind pistons 105 and 105 therein. The pistons are thus forced forwardly of the cylinders, whereupon the retracting arms 100 and 100 are rotated clockwise and counterclockwise, respectively (Fig. l), about pivot points 101 and 1(11, resulting in counterclockwise rotation of ring gear 111 and clockwise rotation of ring gear 111', only the former of which is shownin detail (Fig. 6), and forward rotation of hydrofoil mechanisms 12 and 12.

In tracing the movement of hydrofoil mechanisms 12, for example, to retracted position, initial counterclockwise rotation of ring gear 111 by gear segment 110 (Fig. 6) causes the gear to rotate relative to frame member 53 and to gudgeon 51, whereupon cam surface 112 on the" ring gear rides upon cam surface 113 on the gudgeon, which movement causes the ring gear to slide upward (Fig. 3) relative to the frame member and to nearvertical shaft 58 and until the vertical `surface of cam 114, on the upper surface of the ring gear, contacts the keys 115 secured to the frame member. During this initial counterclockwise rotation and upward movement of yring gear 111, the cylindrical or outboard ends of steering arm 70 and adjusting arm 80 are moved upward relative to frame member 53 and shaft 58 against the downward force of spring 116 and from the position shown in Figs. 4 and 5 to that shown in Fig. 3, which vertical movement disengages the clutch and renders the frame member free to rotate about shaft 58 and relative to steering arm 70 and adjusting arm 80.

Now then, with the vertical surfaces of cams 114 in contact with keys 115 (Fig. 3), the ring gear 111 is no longer free to rotate relative to the frame, so that continuec rotation of the ring gear by gear segment 1-10 (Fig. 6) causes forward rotation of frame member 50 and attached hydrofoil 60 about the now stationary shaft 58. Since shaft 58 andattached bevel 63 are now held stationary, forward rotation of frame 50 about shaft 58 results in rotation of bevel gear 62 and attached horizontal shaft 59 relative to frame member 54, whereupon hydrofoil 60, which is rigidly secured to horizontal shaft 59, is rotated backwards and upwards at a rate, determined by the gear ratio, of slightly more than twice that of the frame. Thus, as a result of a frame rotation of forward, the hydrofoil rotates 180 'backwards and upwards, describing a simultaneous and combined rotation. At the end of this travel, the foil frame retracts to a forward position against the hull of the craft, whereas the hydrofoil itself rotatesinto a nearly-vertical upside down position in line withthe near-vertical axis of rotation of the foil frame, as shown in broken lines vin Fig. 9.

Ihe safety pin 91 (Fig. 7) is incorporated between the splined sleeve and the reduced portion 58d-of shaft 58 vto limit impact on the foil. That is, should the foil striker a` floating object or the like, the pin 91 is sheared, thereby relieving the mechanism of undue strain. To realign the hydrofoil, it is required only to use a portable wrench on the top of. shaft S8 to reset the foil and replace the safety pin. This operation can be performed while aoat.

The angle of attack of hydrofoil 60 may be changed with respect to the frame 50 by means of worm gear 84, attached to arm 70. Rotation of the worm gear by crank 87 rotates arm 80 and shaft 58, with respect to frame 50.I Through bevel gears 62 and 63, shaft 58 rotates shaft 59, and thus hydrofoil 60. All this takes place while frame 50 is held in one position by arm 70 and ram 14.

A feature which permits automatic angle of attack adjustment for control of the bank while turning is the inclination of the near-vertical shaft 58 up and outboard of the hull (Figs. 2 and 4). While steering, the hydrofoil on the outside of the turn moves forward, and the hydrofoil on the inside of the turn moves aft. The up and outboard inclinations of the near-vertical axis of the hydro-` foil frames cause the foil angle of attack to increase on the outboard side of the turn and decrease on the inboard side, thus increasing the lift on the outboard foil and decreasing the lift on the inboard foil. The ditference in the lift forces on the two foils causes an inboard-banking moment which opposes the outboard-banking moment of the boats centrifugal force on the turn. The angle which this axis of rotation makes with the vertical determines the amount of inboard-banking moment of the foils, and so determines how much `the boat banks inboard or outboard A feature which reduces the size of the shafts, bevel gears and clutch members, is the torque-balancing effect of the foils forward of the foil frame. In ight, the forward-rotating moment of the lift caused by the offset strut 67 counteracts, or more than counteracts the aftrotating moment about a horizontal axis in the foil frame of the drag, thus leaving a small residual moment to be controlled by the adjusting arm 80 throughgears 82 and 84 (Fig. 7), as noted above. If the lift torque forward more than counterbalances the drag torque aft, the net torque is then forward, and it provides a cushion for impact on the foils. The impact, when the foils strike an object, has first to overcome the net torque forward before it acts on the shear pin 91.

As will now be seen, the hydrofoil steering, retracting and adjusting mechanism is relatively compact in contiguration, allowing the foils to retract close to the hull out of the water and thus avoid damage to such foil mechanism. The separate hydraulic systems, one for steering and another for retracting, permit diversification of installation, while using the same mechanism for steering, adjusting angle of attack and retraction of the hydrofoils.

asa/,osi

The mechanism is integrated to a degree of allowing al1 necessary functions to 'be Vaccomplished with less parts than heretofore required. The mechanism distributes the lift forces and moments of the foils to the hull in a wider and more effective manner, utilizing existing structural members of the'hull to full advantage. Also, the angle of attack and position of the foils is adjusted and indicated ina positive manner from' the deck of the boat While waterborne.

Without further description it is thought that the features and advantages of the invention will be readily apparent to those skilled in the art to which this invention appertains, and it will, of course, be understood that, while but one embodiment of the invention has been i1- lustrated and described herein, changes in form, proportionsand minor 4details of construction may be resorted to without departing from the spiritof the invention and scope of the' claims.

What is 'claimed is:

l. A hydrofoil craft comprising a hull,a pair of hydrofoils for supporting the craft in motion, means rotatably mounting the hydrofoils one on each side of the hull for rotary movement fore and aft `of the. hull, steering mechanism mounted on the craft, means connecting the steering mechanism to teach of the hydrofoils in a manner such that movement of the steering mechanism in one direction causes forward movement of one hydrofoil and aftv movement of the other hydrofoil, whereas movement ofthe steering mechanism in an opposite direction causes aft movement of the one hydrofoil and forward movement of the other hydrofoil, and means independent of the steering mechanism for retracting the'hydrofoils each to a position for'hull-borne operation of the craft.

2. A hydrofoil craft as set forth in claim 1 wherein the means connecting the steering mechanism to the hydrofoils includes an hydraulic system energized by movement of the steering mechanism.

3. A hydrofoil craft as set forth in claim `1 wherein the means connecting the steering mechanism to the hydrofoils includes a rst hydraulic system energized by move- Cit 8 tive independently of the steering mechanism for simultaneously moving the hydrofoils forward of athwartship to thereby retract the hydrofoils for hull-borne operation of the craft.

5. A hydrofoil craft as set forth in claim 4 wherein the means mounting the hydrofoils on opposite sides of the hull includes a pair of frames, means mounting the frames on opposite sides of the hull for rotary movement about near-vertical axes, means mounting the hydrofoils on the frames for rotary movement therewith about the near-vertical axes and for rotary movement relative thereto about substantially horizontal axes.

6. A hydrofoil craft as set forth in claim 4 wherein the means mounting the hydrofoils on opposite sides of the hull includes a pair of frames,means Amounting'the frames on opposite sides of the hull for rotary movement about near-vertical axes, and means mounting the hydrofoils on the frames for simultaneous movement therewith about the near-vertical Aaxes and for movement relative thereto about substantially horizontal axes, whereby the frames are moved into substantial alignment with the sides of the hull and the hydrofoils are moved into upside down positions for hull-borne operation of the craft.

7. A hydrofoil craft comprising a hull, a pair of hydrofoils for supporting the hull in motion and for steering the craft, means mounting the hydrofoils on opposite sides of the hull for fore and aft rotary movement relative thereto, said mounting means including a frame, anearvertical shaft mounting the frame on the hull and a substantially horizontal shaft mounting the hydrofoil on the frame, means releasably locking the frame tothe nearvertical shaft for movement therewith and for movement relative thereto, steering mechanism mounted'on the craft, means connecting the steering mechanism to the nearvertical shaft for rotary movement of said shaft and frame member as a unit, and means independent of the steering mechanism yfor disengaging the frame from the near-vertical shaft for movement relative thereto, for thereafter rotating the frame about the near-vertical'shaft and for rotating the horizontal shaft and attached hydrofoil about the frame.

References Cited in the file of this patent UNITED STATES PATENTS 1,095,166 Richardson Apr. 28, 1914 2,708,894 Hook May 24,1955 v2,795,202 Hook -..June 1l, 1957 FOREIGN PATENTS 738,333 Great Britain Oct. 12,` 1955 

